1. Field Of The Invention
The invention refers to a laser apparatus in accordance with the gas transport principle with a fast longitudinal gas flow.
2. Prior Art
The efficiency, the amplification and capacity of the molecular lasers, in particular of CO.sub.2 lasers, decrease with increasing temperatures in the laser gas. The reduction of the efficiency is due to the fact that with rising temperatures the line width becomes larger, the excitation energy is distributed among an increasing number of rotation levels, that the number of desactivating collisions increases and that the occupation of the laser end level increases by thermal excitation which results in a decrease of inversion. (K. Gurs, "Laser 74 Opto-Electronics", Conference Proceedings, pages 30 to 37).
Therefore, methods have already been developed which carry of the heat together with the laser gas by circulating and cooling the gas. Suitable lasers consist of an active region in which the gas is excited, with an adjacent or integrated optical resonator, of a gas transport system with a built-in cooler and a pump. Since large amounts of heat have to be carried off, large gas volumes must be circulated by pumping. Corresponding known lasers are large and expensive, and their use is limited because of their bulkiness.
This disadvantage is especially obvious in lasers with longitudinal flow where--as far as known systems are concerned--long gas lines are required. In addition, these pipes cause a correspondingly high flow resistance. Therefore, the efficiency of the system is reduced or especially large pumps will be necessary.
In systems with transversal flow, the interaction path of excited active molecules in the laser resonator is relatively small. Since the power density of lasers is not much above the saturation power, excitation energy is lost in this way, and the lasers have a comparatively low efficiency of for example less than about 10 percent. Furthermore, the transversal excitation is relatively inhomogeneous, resulting in unfavourable radiation characteristics.
The above-mentioned disadvantages of known gas transport and/or convection lasers have already been eliminated in systems where the laser chamber is designed as a cooled pipe which is arranged concentrically within one circulation turbine (German Patent Application, Publication No. 31 21 372). This actually represents an important improvement compared with known gas transport lasers with longitudinal gas flows. However, a large technical effort is required in order to realize such laser.
Especially expensive, even in a large-scale manufacture, are the following four components:
The bearing. Because of the large diameter in the event of exterior bearings and the high rotating velocity, there exists a very high velocity of movable parts against fixed parts. The problem was solved by the use of gas bearings.
The drive. Being a fast running system (400 rotations/second) with hollow inner drive assembly, the engine represents an expensive special construction.
The blading. The circulating compressor is a special construction as well. It is especially unusual and difficult to manufacture the turbine blades fixed to a rotating exterior pipe. Even the use of radial compressors does not result in any important simplification because of the complicated gas transport.
The cooling system. This component is an expensive construction unit because of the circle symmetrical configuration and the necessity of a high cooling power.
Known gas transport lasers use pumps and blowers of different types, e.g., rotary vane pumps, roots blowers (K. Gurs, "Laser 75, Opto-Electronics", Conference Proceedings, p. 30 to 37, or H. Herbrich and B. Dellith, German Patent Application, Publication No. 29 25 829), reactive current ventilators (J. D. Foster, U.S. Pat. No. 4,009,143) or radial blowers (H. J. Seduin and G. Sedgwick, Appl. Optics 11, 1972, 745-748, or K. Sasaki et al., European Patent Application 80 100 870.7, Publication No. 0 015 003). In all cases, the different components must be separately identified as partial systems with defined functions.